“It is time for the administration to first, take responsibility for their mismanagement and second, and most importantly, take responsibility for willfully misleading lawmakers,” Sen. Joseph Brannigan, D-Portland, said at a news conference while flanked by about two dozen Democratic lawmakers.

Brannigan also asked for an investigation by the Government Oversight Committee.

Republicans dismissed the attack, coming in an election year and as late-session tensions rise, as unfounded and partisan.

But it was early March, weeks after the questions were raised, that Department of Health and Human Services Commissioner Mary Mayhew acknowledged the glitch, attributed to the failure of a computer that pays bills to communicate with one that deals with eligibility.

“I use the word cover-up and I know people don’t like that, but the fact is someone knew information that should have been given to all the people on Appropriations,” said Brannigan, who also charged administration officials with “lying several times.”

Democrats acknowledged that DHHS computers have been plagued by problems since the previous administration of Democrat John Baldacci. But they said their main concern is that they weren’t told this time.

“Where else have we been misled?” said Rep. Linda Sanborn, D-Gorham.

Republicans distributed a time line showing that the computer billing systems began operating in September 2010 but staff soon learned that it was not operating correctly. According to the time line, Mayhew was told of a “systemic problem” in February 2012 and on March 1 she was given a detailed briefing that showed the potential impact.

Mayhew briefed legislative committees on March 6, the time line said. A phone and email message left for Mayhew was not immediately returned, but Republicans defended the commissioner’s actions amid difficult budget deliberations.

“My take on this is that they have just made an incredibly serious and extraordinarily outrageous allegation, charging that a cover-up exists without coming up with any tangible evidence to back it up,” said Sen. Richard Rosen of Bucksport, the GOP chairman of Appropriations, who sat through the news conference.

Rosen said the charges seem to call into question all of the work done by the committee to finish the budget. But he said that even if information about the computer problems had been known, “it wouldn’t have changed any of what we did.”

The charges threaten to sour the atmosphere as lawmakers continue making changes to the budget, which calls for additional cutbacks in MaineCare.

LePage’s reaction to the charges was muted.

“It’s a partisan political attack,” said his spokeswoman, Adrienne Bennett.